Metal castings are commonly manufactured through a process referred to as green sand molding. The process entails the steps of compressing sand mixed with a binding agent within a flask and around a matchplate. The matchplate typically includes a plurality of protrusions corresponding to the desired shape of the metal casting to be formed. The matchplate has complementary protrusions on the upper and lower surfaces thereof wherein the upper protrusions extend into a cope flask, and the bottom protrusions extend into a drag flask. Squeeze heads are then positioned above and below the cope and drag flasks to be pressed therein to compress the sand within the flasks and around the patterns protruding from the matchplate.
After the green sand is compressed within the cope and drag flasks around the matchplate, the compressed sand within the cope flask is removed to form the cope mold, while the compressed sand within the drag flask is removed to form the drag mold. The cope mold is then placed on top of the drag mold to form a single sand mold, wherein the internal cavities within the cope and drag molds combine to form the overall cavity having the shape of the desired casting. The cavity can then be filled with molten metal and allowed to cool to result in a metal casting. Prior art systems of this type are well known and disclosed in Hunter U.S. Pat. No. 3,406,738 for "Automatic Matchplate Molding Machine"; Hunter U.S. Pat. No. 3,506,058 for "Method Of Matchplate Molding"; Hunter U.S. Pat. No. 3,520,348 for "Fill Carriages For Automatic Matchplate Molding Machines"; Hunter U.S. Pat. No. 5,156,450 for "Foundry Machine And Method In Foundry Mold Made Thereby"; and Hunter U.S. Pat. No. 5,022,512 for "Automatic Matchplate Molding System", each of which are assigned to the present assignee.
In order to form metal castings having a desired shape, the protrusions on the matchplate must form cavities within the cope and drag molds in exact alignment. Not only must the protrusions be dimensioned to have the exact size and shape of the desired casting, but the formed cope and drag molds must be assembled in exact alignment such that the cavity within the cope mold directly aligns with the cavity formed in the drag mold. Even slight shifts in the cope mold with respect to the drag mold on the order of a few thousandths of an inch will form ridges in the resulting casting. The outer surface of the casting will not be continuous, but will have a ridge or ledge at the midway point of the casting as a result of the mis-alignment of the cope mold with respect to the drag mold.
In prior art systems, relatively few means have been provided to ensure that the cope mold is directly aligned with the drag mold, and correspondingly that the cavities within the cope mold directly align with the cavities within the drag mold. For example, such detection has typically been performed by the operator simply by visually observing the cope mold with respect to the drag mold and detecting a shift. However, given today's increasingly stringent standards, such visual confirmation that the cope mold and drag mold are aligned, does not result in metal castings having the exact dimensions and specifications required.
Other prior art shift detection methods have required the sand mold to be cut or sliced in sections. Not only is this system necessarily limited to the detection abilities of human sight, but also results in an unusable sand mold negatively impacting on cost-effectiveness and productivity.